The Congressional Research Service's report says drones directly raise concerns about "the extent of government surveillance authority, the value of privacy in the digital age, and the role of Congress in reconciling these issues."

Since drone surveillance (like facial recognition technology) "does not require any physical manipulation of a person or his things," American citizens may not have the benefit of the Fourth Amendment's "unreasonable searches and seizures" protections, the report found.

Currently, drones can be outfitted with high-powered cameras, thermal imaging devices, license plate readers, and laser radar (LADAR). In the near future, law enforcement organizations might seek to outfit drones with facial recognition or soft biometric recognition, which can recognize and track individuals based on attributes such as height, age, gender, and skin color… and will soon have the capacity to see through walls and ceilings.

The Fourth Amendment regulates when, where, and how the government may conduct searches and seizures, but the report points out that "sophistication of drones also has the ability to break down any practical privacy safeguard."